This invention relates generally to spectroscopy and, in particular, to a compact spectrometer capable of a broad spectral range.
There is a continuing need for a simple, compact spectrometer which has a narrow passband and can be used over a broad spectral range. Prism or grating spectrometers may be used to analyze a wide spectral range but require a large physical size to achieve sufficient separation of spectra. While these types of spectrometers may be made smaller, a loss of spectral resolution will occur. Fabry-Perot spectrometers utilizing etalons are capable of very high resolution with small size, but an individual etalon cannot cover a broad spectral range.
To obtain a spectrometer that has small dimensions, a narrow passband, and that can be used over a broad spectral range, a significant improvement over present spectrometer designs must be made.
In the invention, collimated, P-polarized light is made incident on an input surface of an optically transparent material at an angle xcex8INC. The light is transmitted through this input transparent material, and reaches a boundary surface between the input material and an output optically transparent material. The material of the input section is preferably highly dispersive, making Snell component values (n sin xcex8) at the boundary surface markedly different for different wavelengths (colors). The material of the output optically transparent material is preferably of low dispersion and high birefringence, such as is characteristic of calcite, for example. The output optically transmissive material is oriented so that its optic axis is other than normal to the boundary surface and is aligned to maximize the birefringence effect of the material.
Only one wavelength present at the boundary surface has a Snell component value (n sin xcex8) that is tangent to its corresponding index surface in the output section of the invention. Within this output section, the ray vector, (r), for this wavelength, is parallel to the boundary surface.
Because optical energy propagates in the direction of the ray vector, only the narrow range of wavelengths having ray vectors that are substantially parallel to the boundary surface are able to reach an output surface at an end of the output section. This narrow range of wavelengths in comprises the passband which is incident on the detector.